This invention relates to packaging methods and apparatus, and more particularly to a form-fill-seal packaging method and apparatus.
The invention is especially concerned with a method of and apparatus for forming, filling and sealing packages in which a web of flexible sheet packaging material is pulled from a supply and fed over means for forming it into tubing, product to be packaged being provided in the tubing, and the tubing being sealed to form packages.
One type of apparatus in which the invention may be used is a machine of the so-called vertical form-fill-seal class in which a web of flexible packaging material is guided from a supply roll of the material over a forming shoulder, at which it is formed into tubing, the tubing being intermittently fed downward, sealed to form a longitudinal tube seam, and ultimately sealed at package length intervals (and cut into individual packages). Heretofore, there have been four basic subclasses, generally, of this class of vertical form-fill-seal machine in commercial use as follows:
1. The type having a vertically reciprocating carriage carrying a set of sealer bars for sealing the tubing at package length intervals, the bars closing on the tubing generally at the upper end of the upstroke of the carriage, pulling a package length increment of the tubing downward on the downstroke of the carriage, and then opening for the upstroke, as sold by Hayssen Manufacturing Company of Sheboygan, Wis., assignee of this invention, and a number of other companies.
2. The type having belts engaging the tubing on a mandrel to feed it downward in package length increments, with a dwell between successive feed cycles, a set of sealer bars being operable in a fixed horizontal plane below the lower end of the mandrel during each dwell to form a transverse seal across the tubing.
3. The type in which the forming shoulder is vertically reciprocable for feeding the tubing downward in package length increments, with a dwell between successive feed cycles, a set of sealer bars being operable in a fixed horizontal plane during each dwell to form a transverse seal across the tubing.
4. The type having vertically reciprocating vacuum grippers (vacuum boxes) engageable with the tubing on a mandrel, or a vertically reciprocating fin seal gripper (the longitudinal seam for the tubing being a fin seal in this case, as distinguished from a lap seal), for feeding the tubing downward in package length increments, with a dwell between successive feed cycles, a set of sealer bars being operable in a fixed horizontal plane below the lower end of the mandrel during each dwell to form a transverse seal across the tubing.
Problems such as the following may at times be encountered in the operation of packaging machines of these types:
(A) The pull on the tubing required to draw the material over the forming shoulder and feed it downward, i.e., either the so-called "breakaway pull", which is the pull required to start the feed of the material and the tubing following a dwell, or the "continuous pull", which is the pull required to keep the material moving, may be so high for certain materials as to tend to degrade the material, by inducing severe stresses particularly at the shoulder area and may further cause stretching of the packaging material in other instances, and to degrade the material from the standpoint of appearance;
(B) The machine may have to be operated at a lower package production rate than desired; and
(C) The material fails to track properly over the forming shoulder, reducing efficiency of operation.